System for the rapid starting of a mechanism



March 29, 1966 H. ZAHN 3,242,7@5

SYSTEM FOR THE RAPTD STARTING OF A MECHANISM Filed Feb. 26, 1963 Attorney United States Patent 3,242,765 SYSTEM FOR THE RAPID STARTING F A MECHANISM Heinrich Zahn, Rossdorf, near Darmstadt, Germany, assignor to Fernseh G.m.b.H., Darmstadt, Germany Filed Feb. 26, 1963, Ser. No. 261,158 Claims priority, application Germany, Mar. 1, 1962, F 36,159 6 Claims. (Cl. 74-572) It is an object of the present invention to create a system and method of rapidly starting a rotating mechanism to an accurately predetermined speed within a short time.

A further object of the invention consists in a system and method of accelerating a film transport mechanism including a synchronous driving motor of relatively low power to a predetermined speed within a time shorter than the run up time of the synchronous motor.

Another object of the invention is a system and method of rapidly starting a television film transport mechanism including a synchronous driving motor rigidly connected with the film transport means to a predetermined speed.

It is often a requirement that small mechanisms which require a relatively small driving torque kfor continuous operation at an exactly predetermined speed shall be capable of being brought very rapidly into a fully operational condition -from a standstill. An example of a mechanism in which this requirement arises is cinematographic apparatus, especially such apparatus used for the recording or reproduction of television signals. In television film scanning apparatus, for example, it is desirable to be able to obtain synchronous speed within a time so short that the `signals derived from the scanner can be faded into ya television transmission by remote control. For this purpose, any interruption of the transmission during the starting of the film scanner must be so brief that it is not perceived by the viewer. This means that the operating speed of the film transport mechanism must be reached in a tenth of a second or less. The power necessary to produce such a rapid acceleration cannot be produced by the small four-pole motor usually provided to drive film transport mechanism, since such a motor cannot be suiciently accelerated within one or two periods of the -alternating current supply.

One way of overcoming this difficulty is to disconnect the motor from the mechanism which it drives and to bring the motor to an appropriately high speed immediately before it is required to start the mechanism, engaging the motor with the mechanism only when it is required to start the latter. This method is not always applicable, and in particular is not useful in the case of film scanning apparatus, since the clutch necessary to engage the motor with the film transport mechanism introduces an indeterminate phase relation between the motor and the transport mechanism. This uncertainty of phasing cannot -be allowed, since it is necessary lfor the operation of the film transport mechanism to be exactly correctly phased with respect to the alternating voltage supply to the drive motor and hence to the field fiyback process in the television picture.

The present invention seeks to provide a solution to the problem of producing rapid and continuous acceleration of a mechanism to a specified operating speed, at which the mechanism is thereafter driven by ya synchronous motor of low power. In particular, the invention seeks to provide a means for the rapid starting of cinematographic apparatus driven synchronously With the mains.

According to the present invention there is provided means for the rapid starting of a mechanism which in operation is driven at a specified speed by a synchronous driving motor continuously connected to said mechanism, comprising a flywheel arranged to Ibe driven at an initial speed substantially greater than said specified speed, and a frictionally engaging clutch arranged when engaged to connect said flywheel to said mechanism, the moment of inertia of said fiywheel and said initial speed being such in relation to the moment of inertia of said mechanism that when said clutch is engaged the mechanism is accelerated to said specified speed during the deceleration of said flywheel from said initial speed to said specified speed.

It is an advantage `of the present invention that the power source required to drive said flywheel may itself be of relatively low power, since there is within reason no limit to the time which may be consumed in yarriving at the initial speed of the flywheel. The power for driving the flywheel is advantageously obtained from a small induction motor which may remain continuously excited before and during the starting process.

A convenient way of carrying out the invention is to couple the flywheel to the mechanism by way of an electromagnetically engaged clutch, for example an electromagnetic disc clutch, which is actuated by an exciting current produced as a result of a local yor remote control operation. When the mechanism has attained the specified operating speed the clutch may be released again, so that the auxiliary motor can no longer affect the speed of operation of the mechanism. If the energy stored in the flywheel is correctly chosen, Very rapid acceleration of the mechanism, specifically of a film transport mechanism, to its specified operating speed may be produced, the specified operating speed being attained substantially without overshoot. lf, on the other hand, the energy stored in the flywheel is not suitably chosen, there may occur a condition in which the mechanism is at first brought to a speed execeeding its specified operating speed and only slowly pulls-in to the required speed. It is true `th-at this disadvantage could be overcome by appropriately controlling the time of engagement of the clutch, but the apparatus necessary correctly to determine the time of engagement of the clutch would necessarily be complex and therefore unreliable.

The required initial speed of rotation ws and the moment of inertia J5 of the fiywheel can be calculated in the following manner, the driving power required by the film transport mechanism and the heat produced during the process of engagement of the clutch being at first neglected. ILet JM be the moment of inertia of the film transport mechanism, including that of the normal driving motor, while the moment of inertia JS of the flywheel is assumed to include that of the auxiliary driving motor. The specified operating speed 0M of the film transport mechanism may, `for example, be 1500 r.p.m., the initial speed ws to which the flywheel is raised by the auxiliary motor may be 2700 rpm., and the moment of inertia JM of the mechanism may be taken as being 24 [cm. g. secr-2]. If the moments of inertia are considered as being proportional masses mM and ms respectively, then in accordance with established theory for inelastic collision:

gagement and also ignores the continuous power required to drive the mechanism. It may be shown by a more revthat such fluctuations are a minimum if just half of the kinetic energy of the flywheel is dissipated as heat. In this case JS is equal to JM and ws is equal to ZwM.

The invention will now be more particularly described with referenceto the accompanying drawings comprising FIGURES 1 to 3, of which:

FIGURE 1 is a partly sectional elevation of one ern- Abodiment of electromagnetic clutch means suitable for use in carrying out the present invention,

FIGURE 2 is a circuit diagram of an arrangement suitable foroperating the clutch described in relation to FIG- U'RE 1, and i FIGURE 3 is a graph illustrating the action of the circuit described in relation to FIGURE 2.

In FIGURE l an auxiliary motor 1 carries on its shaft a flange 2 from which project pins such as 3 engaging in mating holes in an elastic annulus 4. Annulus y4 has other holes in which engage pins such as 5 projecting from a flywheel 6 supported by ball-bearings 7 from the drive shaft 8 of a film transport mechanism not Votherwise shown. On shaft 8 there is also mounted a clutch disc 9, which is keyed to shaft 8 at 10 so that both are constrained to rotate together though disc 9 is capable of limited axial movement upon shaft 8 against the action of a return spring 11.

To the boss 12 of clutch disc 9 is secured an armature disc 13 of ferromagnetic material which is placed in the ing speed, while the speed of flywheel `6 is correspondingly reduced.

It is advantageous that the clutch shall be released again vwhen shaft S has been brought to the specified operating speed. This may conveniently be assured by using the circuit arrangement illustrated by FIGURE 2 to provide the exciting current lfor clutch winding 15. Here a capacitor C, which may have a value of 2G00 nf., is charged by by way of a resistor R, which may have a value of 3.5

kit, from a direct voltage source represented by terminals -land which may provide a potential of 4()` volts. When a switch S, conveniently operated simultaneously with the switch which turns on the drive motor for the film pulldown mechanism, is closed, capacitor C discharges into the operating coil 15 of clutch magnet 14. The magnetic field thus produced urges armature 13 towards the magnet against the action of clutch return spring 11 and causes the clutch to engage. Since, however, it is arranged that the value of resistor R is large compared with the resistance of Jcoil 15, the current in the coil diminishes relatively rapidly in accordance with an exponential law, as illustrated by the graph shown in FIGURE 3, finally reaching that value, indicated by broken line 17, at which the clutch is disengaged by the return spring 11. The time lo which elapses between the engagement of the clutch and its release must be somewhat greater than the time necessary for the flywheel to bring the film transport mechanism to its specified operating speed, but again, not so large that appreciable energy is transferred from the auxiliary motor 1 to the shaft 8. In an experimental model of such an varrangement it was lfoundthat the ratio of the power of the auxiliary motor 4 to that of the driving motor could belzZS, yAfter the release of the clutch the current through coil 1'5 sinks to a final value I0 determined by the value of the series resistor R.

What is claimed as new and desired to be secured by Letters Patent is:

l. System for the rapid acceleration of a film transport mechanism including a synchronous driving motor from standstill to a specified speed corresponding to the Vsynchronous speed of saiddriving motor, comprising a main driving shaft connecting said acceleration system to said film transport mechanism, a flywheel rotating on bearings on said driving shaft, an auxiliary motor for driving said fiywhel with an initial speed, an electromagnetic clutch including a clutch disc movably keyed to said shaft and adapted to engage said flywheel, the moment of inertia of said fiywheel and said initial speed being such in relation to the moment of inertia of said mechanism that upon engagement of said clutch such an amount of kinetic energy is transferred from said flywheel to :said mechanism through the engaged clutch that the mechanism is accelerated from standstill to said specified speed and said iiywheel is decelerated from said initial speed to said specified speed, and means to produce disengagement of said clutch after a predetermined time period which is greater than the time period required for said vmechanism and said flywheel to attain said specified speed.

2. System for the rapid acceleration of a film/transport mechanism including a synchronous driving motor from standstill to a specified speed corresponding to the synchronous speed of said driving motor, comprising a main driving shaft connecting said acceleration system to said film transport mechanism, a flywheel rotating on bearings on said driving shaft, an auxiliary motor for vdriving said flywheel with an initial speed, an electromagnetic clutch including a clutch disc movably keyed to said shaft and adapted to engage said flywheel, the moment of inertia of said flywheel including said auxiliary motor being equal to the moment of inertia of said mechanism including said driving motor, and the initial speed of said flywheel being twice the specified speed so that upon engagement of said clutch such an amount of kinetic energy is transferred from said flywheel to said mechanism through the engaged clutch `that the mechanism is accelerated from standstill to said specified speed and said flywheel is decelerated from said initial speed to said specified speed.

3. System for the rapid acceleration of a film transport mechanism including a synchronous driving motor from standstill to a specified speed corresponding .to the synchronous speed of said driving motor, comprising a main driving shaft connecting said acceleration system to said film 'transport mechanism, a flywheel rotating on bear- 'ings on said driving shaft, an auxiliary motor for driving said iiywheel with an initial speed, an electromagnetic clutch including Ian electromagnet, a clutch disc movably keyed to said shaft and yadapted to engagesaid ffywheel, a return spring arranged to produce disengagement of said clutch when the current through said electromagnet of said clutch falls below a given value, the initial speed and the moment of inertia of said flywheel including said auxiliary motor being such in relation to the moment of inertia of said film transport mechanism including said driving motor that upon engagement of said clutch such an amount of kinetic energy is transferred from said liywheel to said mechanism through the engaged clutch that ,the mechanism is accelerated from standstill to said specified speed and said fiywheel is 'decelerated from said initial speed to said specified speed,

chronous speed of said driving motor, comprising a main film transport mechanism, a iiywheel rotating 0n bearings on said driving shaft, an auxiliary motor for driving said iiywheel with an initial speed, an electromagnetic clutch including a clutch disc movably keyed to said shaft and adapted to engage said ywheel, the initial speed and the moment of inertia of said flywheel including said auxiliary motor being such in relation to the moment of inertia of said film transport mechanism including said driving motor that upon engagement of said c-lutch such an amount of kinetic energy is transfer-red from said flywheel to said mechanism through the engaged clutch that the mechanism is accelerated from standstill to said specified speed and said flywheel is decelerated from said initial speed to said specified speed and means to produce disengagement of said clutch after a predetermined time period which is greater than the time period required for said mechanism and said flywheel to attain said specified speed, said means comprising an electric circuit Vfor 'actuating the electroma-gnet of said clutch comprising a condenser, a D.C. voltage source, a resistor, and a switching element, both terminals of said condenser being connected by way of said resistor to said voltage source, one terminal of said condenser being connected directly, the other by way of said switching element to said electromagnet, the time constant of discharge of the condenser through the exciting winding of said electromagnet when said switch is closed being slightly greater than the time in which said mechanism is accelerated to said specified speed, and a return spring arranged to produce disengagement of said clutch when the current through said electromagnet falls be-low a given value.

5. In a system comprising a rotary mechanism including a synchronous motor operating at a specified rotary speed, in combination, an apparatus for rapidly `accelerating said mechanism with said synchronous motor from a standstill to said specified speed including a ilywheel; an auxiliary motor for driving said fiywheel at an initial speed greater `than said specified speed; and a clutch between said fiywhee-l and said mechanism having an engaged condition for connecting said ywhel with said mechanism and synchronous motor, the moment of inertia of said fiywheel and said initial speed having such a rela- 4 upon engagement of said clutch such an amount of kinetic energy is transferred from said flywheel through the engaged clutch to said mechanism `and synchronous motor that said flywheel is decelerated from said initial speed to said specified speed and said synchronous motor is accelerated to said speciiied speed and further maintains said mechanism at said specified speed.

6. In a system comprising a rotary mechanism including a synchronous motor operating at a specified rotary speed, in combination, an apparatus for rapidly accelerating said mechanism with said synchronous motor from a standstill to said specified speed including a flywheel; an auxiliary motor for driving said flywheel at an initial speed greater than said specified speed; a clutch between said fiywheel and said mechanism having an engaged condition for connecting said iiywheel with said mechanism and synchronous motor, the moment of inertia of said flywheel and said initial speed having such a relation to the moment of inertia of said mechanism and said synchronous motor and to said specified speed that upon engagement of said clutch such an amount of kinetic energy is transferred from said iiywheel through the engaged clutch to said mechanism and synchronous motor that said flywheel is decelerated from said initial speed to said specified speed and said synchronous motor is accelerated to said specified speed and further maintains said mechanism at said specified speed; and means for disengaging said clutch a predetermined time period after engagement, said time period being selected to be only slightly greater than the time required for acceleration of said mechanism and synchronous motor to said specified speed so that said synchronous motor is separated from said flywhel when the latter is accelerated by said auxiliary motor above said specified speed.

References Cited by the Examiner UNITED STATES PATENTS 1,102,116 6/1914 Wood 74-572 X 1,147,956 7/1915 Lutz 74-6 X 1,424,987 8/1922 `Clark 74-572 X 2,284,431 5/1942 Kearney 74-7 X 2,730,911 1/1956 Silberstein 74-572 2,913,190 1l/1959 Berthold 74-572 X BROUGHTON G. DURHAM, Primary Examiner. T. W. SHEAR, Assistant Examiner. 

1. SYSTEM FOR THE RAPID ACCELERATION OF A FILM TRANSPORT MECHANISM INCLUDING A SYNCHRONOUS DRIVING MOTOR FROM STANDSTILL TO A SPECIFIED SPEED CORRESPONDING TO THE SYNCHRONOUS SPEED OF SAID DRIVING MOTOR, COMPRISING A MAIN DRIVING SHAFT CONNECTING SAID ACCELERATION SYSTEM TO SAID FILM TRANSPORT MECHANISM, A FLYWHEEL ROTATING ON BEARINGS ON SAID DRIVING SHAFT, AN AUXILIARY ROTOR FOR DRIVING SAID FLYWHEEL WITH AN INITIAL SPEED, AN ELECTROMAGNETIC CLUTCH INCLUDING A CLUTCH DISC MOVABLY KEYED TO SAID SHAFT AND ADAPTED TO ENGAGE SAID FLYWHEEL, THE MOMENT OF INERTIA OF SAID FLYWHEEL AND SAID INITIAL SPEED BEING SUCH IN RELATION TO THE MOMENT OF INERTIA OF SAID MECHANISM THAT UPON ENGAGEMENT OF SAID CLUTCH SUCH AN AMOUNT OF KINETIC ENERGY IS TRANSFERRED FROM SAID FLYWHEEL TO SAID MECHANISM THROUGH THE ENGAGED CLUTCH THAT THE MECHANISM IS ACCELERATED FROM STANDSTILL TO SAID SPECIFIED SPEED AND SAID FLYWHEEL IS DECELERATED FROM SAID INITIAL SPEED TO SAID SPECIFIED SPEED, AND MEANS TO PRODUCE DISENGAGEMENT OF SAID CLUTCH AFTER A PREDETERMINED TIME SPACED WHICH IS GREATER THAN THE TIME PERIOD REQUIRED FOR SAID MECHANISM AND SAID FLYWHEEL TO ATTAIN SAID SPECIFIED SPEED. 